Cathode-ray tube apparatus



Nov. 23, 1948. s. v. FoRGUE 2,454,378v

CATHODE-RAY TUVBE APPARATUS Filed May 28, 1945 ATTORNEY.

Patented Nev. 23. 194s CATHODE-RAY TUBE APPARATUS Stanley V. Forgue,Princeton, N. J., assignor to Radiov Corporation of America, acorporation of Delaware Application May 2s, 1945, serial No. 596,206 7ciai'ms. (o1. 315-31) The present invention relates to cathode ray tubeapparatus and more particularly to an arrangement for obtaining combinedstatic and dynamic alignment, or dynamic alignment separately, of thecathoderay scanning beam in a cathode ray tube.

In a cathode ray tube, particularly of the low beam velocity type, it isdesirable for proper operation of the tube that the electrons composingthe cathode raybeam approach the target in a direction which issubstantially normal to rthe Asurface of the target.M This requirementholds for tubes in which `the electrons actually land on the target,usually with substantially zero velocity at the time of landing, or intubes, the elements of whichare so biased that all of the electrons inthe beam do not actually land .on the target butin which'some of theelectrons are selectively deflected fromthe target to provide an imagesignal. Mechanical non-uniformity of manufacture and pos-siblearbitrarily imposed `operating conditionsprevent uniform normal landingof the beam over all parts oi the target electrode of the tube. At anyone part of the target, normal incidence of the beam is obtained inaccordance with the present invention by introducing a distortion at theelectron gun to provide a departure from normal incidence which isequal'and opposite to the departure caused by' non-uniformity ofmanufacture or by arbitrarily imposed operating conditions. Applicationof an externaleld for another purpose is described in United StatesPatent No. 2,224,933, granted to Kurt Schlesinger on December 17, 1940.The present invention' provides for phasing the corrective distortion:of the scanning beam so that normal incidence is insured for all pointsof the target. Electrical currents which `produce this distortion may,in general, have the same form a-s the scanning currents. In some cases,arbitrary current configurations may be desirable. and the provision ofsuch currents and their use is within the scope of the presentinvention. The varrangement of `the present invention may beemployedwith any cathode ray` tube in which deflection is symmetrical about theaxis and, also, in other tubes where there is a change in Wave form ofthe deecting current-s or voltages to correct for distortion of the`scanning pattern. A common form of distortion whichl is corrected by awave form change is known as keystoning For each position of-.thescanning electron beam on a cathode ray tube target there is `an optimumvalue of'thebeam alignment as it leaves the electron gun.V The dynamicalignment arrangement or system of the invention, mentioned generallyabove, makes it possible more `nearly to obtain this optimum value thanis possible with conventional static alignment systems.

p The primary object of this invention is to produce normal incidence ofa cathode ray beam atl all points of a Scanned target within a cathodevray beam tube.

Another object is to provide a dynamic alignment system for the cathoderay beam in cathode ray tubes. Y

Still another object is to provide a combined static and dynamicalignment system for the cathode ray beam in cathode ray tubes.

A further object is to provide an arrangement for producing a resultantmagnetic flux in a direction substantially perpendicular to the cathoderay beam of a cathode ray tube, the radial direction of the resultantbeing adjustable to compensate for initial misalignment of the beamsource and/or it-s associated parts.

A still further object is to produce a periodically varying resultantiield in a direction substantially at right angles to the cathode -raybeam of a cathode ray tube for the purpose of accomplishing static anddynamic alignment of a cathode ray beam. v

Other and more specific objects of the inventionrwill become apparentand suggest themselves to those skilled in the art to which theinventionl is directed upon reading the following specification andclaims in connection with the drawings in which:

Fig, l shows, conventionally,` one type of cathode ray tube providedwith a combined static and dynamic alignment system in accordancewiththe invention; l

Fig.` 2 is a sectional view taken on line 2-2 of Fig. l, together with aschematic showing of operating circuits Vfor the combined alignmentsystem;

Fig. 3 is a sectional View of a modification;

Fig. 4 is a sectional View of another modification together with itsoperating circuits; and

Fig. 5 is a series of curves' referred to in the operation of apparatusembodying the invention.

Referring for the present to Figs. l and 2 of the drawings, an alignmentsystem in accordance with the invention is shown a-s being applied to acamera tube I0. The tube I0, selected for purposes of illustration, isof the high sensitivity low beam velocity type knownas the ImageOrthicon. The image type of Orthi-con is disclosed and claimed in thecopending application forU. S. Letters Patent of Albert Rose, SerialNo.-

3 407,132, led August 16, 1941, now Patent #2,403,239. An Orthicon ofthe low beam velocity type is disclosed in United States patent to Rose,No. 2,213,176, granted August 27, 1940, and Orthicons of the return beamtype are shown in United States patents to H. A. Iams, Nos. 2,213,177and 2,288,402, granted August 27, 1940, and June '30, 1942,respectively. In lthe tube I0, a target I6 is to be scanned by a lowvelocity electron beam I8 produced by an electron gun I'9. The target I6may be of the type di-sclosed in the copending Rose application abovereferred to operating in -conjunction with a photocathode I5 provided inthe end wall of the tube.

Fig. 1 includes a schematic showing of a magnetic deecting yokeincluding horizontal and vertical deecting coils 2I and 22,respectively. A focusing coil 23 surrounds the tube and provides anaxial focusing field for the low velocity beam I8 in a manner which isby now well known and is discussed in the copending application and thepatents above referred to. Also, the functions and connections of theseveral electrodes of a tube such as Ythe tube I .are disclosed in thepatents above referred to and more particularly in a .copendingapplication for U. S. Letters of Patent of Paul K. Weimer, Serial No.544,494, filed September 16, 1944, now Patent No. 2,433,941. A furtherand more detailed description of the tube I9, therefore, is deemedunnecessary since the present invention is concerned with the alignmentof the beam I8 after it emerges or is projectedfrom the gun I9.

It is preferred in a tube of this ,kind that the undeflected beamapproach the target I B at the center thereof or at least inthe centerof a desired scanning raster. It will be understood that electrons ofthe beam also may land upon the target with substantially zero velocity.As pointed out above, non-uniformities of tubemanufacture can in manycases cause the undeflected beam to approach .or land at some angle tothe normal at a point other than the center of the target or the centerof the scanned raster, and when the beam is deflected, cause the beam toapproach the target from an angle other than the desired right angle. Amisaligned beam may still land at the center of the target if the latteris biased to a sufficiently positivepotential. However, thebeam'possesses helical motion as a result of the misalignment whichcauses it to approach the target at non-normal incidence, so that with anormal positive bias on the target, the beam may fail to land because ofthe transverse velocity components it possesses as a result of thishelical motion.

The beam I8, as shown in Fig. 1 of the drawings, is indicated as havingbeen deflected by the magnetic deilecting yokevpreviously referred to,the solid line designating the desired normal landing ofthe beam. Thedashed line indicates a departure of thefbeam to an exaggerated degreefor the sake of illustration. Such-a departure might occur because "ofunavoidable misalignment of the tubeparts during manufacture. The anglea indicates the degree of this departure, and in accordance with theinvention, four coils 29, 30, 3I,'and 32 are arranged to surround theneck of the coil near the position where the cathode ray beam leaves thegun I9. The function of these coils is to introduce transverse velocitycomponents which cancel objectionabletransverse velocity componentsintroduced elsewhere, for example, because of beam misalignment. Thecoils 29 to 32 are arranged in pairs and are carried so as to bemechanically rotatable as a unit in any desired manner known in theprior art, for example by being embodied in a yoke structure such as isused to provide deection of a cathode ray beam in a Kinescope or anIconoscope The mounting shown is illustrative and comprises a tubularmember 34, preferably, although not necessarily, of insulating materialwhich closely surrounds the neck of the tube Il). Means indicated as afinger piece or handle 36 provides for rotating the tubular member 3Aand the coils located thereon as a unit to give the best adjustment forobtaining the most uniform beam landing over the entire raster. Rotationof the coils 29 to 3| as a unit provides dynamic alignment of the beamas this'function will be referred to hereinafter. Directcurrent is fedinto the coils 29 to 32 as well as alternating currents having a desiredwave form in a manner now to be described.

A multi-contract Ipotentiometer 38 comprises a continuous circularresistor having sectionsvg39 and 40 which are oppositely disposedgeometrically. These sections are connected in parallel across Aanysuitable source 93y of direct current. The pair of coils 29 and 30 arejoinedtogether in series and are connected tothe slidable contacts 4Band lt'l over conductors 48 and 49. A choke coil 52 is included in theD. C'. path through thecoils 29 and vv392m series'to block outalternating currents introduced in these coils in a manner to bedescribed. The pair ,of coils '3| and 32 is connected .to potentiometercontacts 5'4- and 55 over conductors 58 and 51, this connectionincluding a choke coil 59. The contactsv 65,41, 54 and'55 are `rotatabletogether by any suitable means such as indicated schematically at 80.Rotation of these contacts will vary the position of the resultant'feldproduced by the two sets ofcoils and continued rotation of thesecontacts will varyy the phase or sense of the resultant. Staticalignment" is provided by changing the position and/or sense of theresultant field.

A variable resistor=62 mayibe used to vary the current 'flowing throughVthe potentiometer Aresistors'which, in turn,y determines the voltagediiference across these resistors.

In place of the-'multi-contact potentiometer, shown by wayof example,-direct current may be fed into each pair of coils throughvariableresistors and reversing switches- A sawtooth current from-the sourcewhich supplies the coils 2|, for example, is fed through the coils 3land v32 in series. This-'may readily be accomplished as shown in Fig. 2vofthe drawings, "for example, by providing a variable resistive shunt'64 across terminals V36 which are in communicationwith the horizontaldeilection source for thetube I0. A condenser' 68 preventsshortcircuiting of the direct current path through the coils. A verticalsawtooth'wave applied to terminals 10 is fed to the coils '29` and "'30under control of Ya shunt-connected variable resistor T2. A condenser"I3 prevents lshort circuiting of the D. C. path'through the coils`29`and 39.

'In operation ofthe arrangement disclosed in Figs. 1 and 2 ofthedrawingsthe pair`2'9 an'd'30 and the pair 3| and 32 of -coilsaremechanically rotated as a unit to an approximate rotational positionpreviously determined by successive approximations for best 'beamlanding at the edges of the target. 'In general, Vfor like tubes therotational position of Vthese dynamic alignment coils should 'not haveto be altered appreciably going from tube to tube, other things relevantto the tube operation remaining unchanged.

The rotational position of the resultant ofthe ux set up by the coils"29and 30 and the coils 3l and 32 provides for static alignment and thisresultant is adjusted electrically by means of the multi-contactpotentiometer 38 to give the best operation at the center of the target.Thefcenter operation of the undeected beamfis further improved byvarying the current through the coils by changing the setting of thevariable resistor 62. The magnitude of the ,sawtoothcurrent in the coils3| and 32 which produces a ilux to serve for horizontal dynamicalignment purposes is adjusted for the best operation at the edges ofthe target. This adjustment isperformed by changing the setting of thevariable resistor` 6,4. 'The edge operation is further improved =bysuitably adjusting the magnitude of the sawtooth current component inthe coils 29 and 30. `This is accomplished by adjusting the resistor 12.The steps set forth immediately above are repeated until the bestover-all operation isobtained.

Referring to Fig.` 5 of the drawings and considering either thehorizontal or vertical deection voltage wave` as beingrshown by curve76, vwhen this wave or thedeecting eiTect onthe cathode ray beamv of theflux produced by this wave passes through zero, then in a theoreticallyperfect tube I0 of the type shown in Fig. l, the beam will be at the`geometrical center of the raster which is to be traced on the targeti6. Moreover, the beam will approach or land on the target from adirection normal thereto. Curve 18 indicates the current, or itsmagnetic effect on the cathode ray beam, which is supplied to a pair ofcoils, either coils 29 and 3D or coils 3l and 32, `simultaneously withthe wave represented by the curve 'l6.` The point on the L 38, themagnitude of the displacement of the Vcurve 'i8 being determined byadjustment ofthe resistor $2. Movement of the entire yoke by the handle36 accomplishes mechanical rotational alignment for the dynamicalignment system.v The angular position of the potentiometer contactsaccomplishesrotation of the resultant field which provides staticalignment as a result of the application of the sawtooth waves,

`Fig. 3 of the drawings indicates an arrangement in which both thestatic alignment system comprising a pair of coils 8| and 82 and thedynamic alignment system comprising two pairs of coils 84 and 85, and 86and 87 are rotated rnechanically. The static alignment coils 8l and 82may be mounted upon a tube or yoke 89 which may be rotated by ahandle orthumb piece 9|. The dynamic coils 84 to 87 are carried by a yokecomprising the tubes 9d and 95 rotatable upon movement of a thumb pieceor a handle 98. The coils 8l and 82 are supplied with direct currentwhich may be varied at will for adjustment in any suitable manner. Thecoils 86 and 81, corresponding to the coils 29 and 3l] of Fig. 1, arefed from the vertical sawtooth input with means, such as the means 12,shown in Fig.

2ior adjusting the strength of the field produced" by the sawtoothcurrent in these coils. The coils 84 `and 85 likewise carry anadjustable current derived from the horizontal sawtooth input.

It will be seen that the arrangement of Fig. 3 provides a pair ofcoilsnamely coils 8| and 82, for static alignment with mechanicalrotation of this separate pair and mechanical rotation of the two setsof vdynamic alignment coils as a unit. i

Fig. 470i the drawings shows an arrangemen which'is similar to Fig. 3except that electrical rotation of the static alignment eld is providedby a pair of coils IDG and lili, operating in conjunction with anassociated pair of coilsv |92v and ID3. The resultant eld produced bythese two pairs of coils is rotated by adjustment of a multi-contactpotentiometer H36 similar to the potentiometer 38 of Fig. 2. A variableresistor |08 provides for independent adjustmentof the magnitude of theresultant eld which provides static alignment of the beam. Dynamicalignment is provided by a pair of coils |99 'and H0 operating inconjunction with a pair of coils lil and H2. The coils IBS and H0correspond to the coils 86 and 8'! of Fig. 3, while the'coils lll and H2correspond tothe coils 84 and 85 of-Fig. 3. i A'fmger piece or handle H6serves to rotate the dynamic alignment coils as a unit.

While magnetic arrangements for securing static and dynamic alignmenthave been shown by way of example, it will be understood that voltagedeection plates rather than coils may be used. These plates will belocated in the same region as the coils, several examples of which havebeen described above, and will preferably be short as compared with vthedistance between two successive focal points of the beam. AV set ofoppositely disposed plates may be employed to which is fed the verticaldeecting sawtooth voltage wave after amplification in an amplifierhaving a readily operated gain control. Likewise, a cooperating pair `ofoppositely disposed plates displaced 90 from the plates havingthevertical deiiectingrsignal applied thereto would be provided. )Thehorizontal deecting signal is fed also by way of a controlled am"-`pliiier to these cooperating plates. Both sets of plates are preferablyrotated as a unit.

Having now described the invention, what is claimed and desired to besecured by Letters Patent is the following:

1. In combination, a cathode ray tube having a target and means forproducing and directing a cathode ray beam toward said target. means forproducing scanning deiiection of said beam to cover a bidimensionalpattern, means for insuring i the landing of said beam when a deflectioneffect is absent at substantially the center of said target whereby saidbidimensional pattern will be centered upon said target comprising meansfor producing a beam influencing eld transversely of said tube, means tochange the direction of said eld, and means to change the polarity ofsaid leld.

2. The combination of claim l wherein means to change the strength ofsaid beam inuencing field are present.

3. In combination, a cathode ray tube having a target and means forproducing and directing a cathode ray beam toward said target, means forproducing scanning deflection of said beam to cover a bidimensionalpattern, means for insuring the landing of said beam at substantiallythe center of said target whereby said bidimensional aeg-4,878

pattern-will be centeredwith respectto saidtarget, opposed lpairs ofycoils to provide a resultant magnetic eld transversely of said tube,connections for energizing said pairs of coils, and a multi-contactpotentiometer included in said connections for reversing the rdirectionof the current flowing in said coils and for controlling the strengththereof whereby to alterthe direction and polarity of said resultantvtransverse field.

4. In combination, a cathode ray tube having a target andmeans forproducing and directing a cathode ray beam toward-said targetymeans forproducing scanning deilection of said beam to cover a bidimensionalpattern, means for insuringthe landing of said beam -at substantiallythe centervofsaid target wherebysaid bidimensional pattern will becenteredupon ysaid target cornprisingopposed pairs of coils lto providea magnetic leld transversely of said tube, an operative connection forenergizing said pairs of coils With unidirectional current, meansv forvsupplying one pair of coils with alternatingcurrents of a wavefforrnsimilar to ythat `which produces one component of the bidimensionalpattern, means for supplying the other pair of coils with alternatingcurrent of Va wave form similar Ato that which produces the othercoordinate of the bidimensional pattern whereby to add in insuringperpendicularity of said-beam to said target at all points of thebidimensional pattern.

15. Incombination, la. cathode ray tube'having a target randmeans forproducing land directing a cathode raybeam'toward said target,'rneansfor producing scanning deflection of said beam to cover abidimensionalpattern, twopairs'of oppositely disposed coils, each -pair of coilsbeing positioned on an axis substantially at right angles to the axisyof the other pair of coils, la mounting for said coils surrounding saidtube and being rotatable with 'respect thereto, terminal connections`for supplying Said coils -With unidirectional current whereby thelocusof the scanning pattern of the beam with 4respect to the target maybe adjusted, said pairs of coils 4being rotatable as a unit whereby'theportionof .the beamradjacent to the target is brought normal tothetarget at the edges of the target.

6. In combination, a cathode ray tube having av target and means forproducing and directing a cathode ray beam toward said target, meansfforproducing scanning deflection of said .beam Vto covera bidimensionalpattern, two. pairs of oppositely disposed coils, each pair of coilsbeing positioned on an axis substantially .at rghtangles to the axisofthe other pair of coils, meansior Asupplying onepair ofcoilswithalternating Ycurrents of a wave-form similar-to that whichproduces onecoordinate of .the scanning movement, ,and means to supply the otherpair of vcoils with alternating current, of a wave form similar to thatwhich produces the other coordinate of scanning movement of the beamwhereby -to insure -perpendicularity of the beam with respect tothetarget.

7. In combination, a cathode ray tube having a target and means forproducing and directinga cathode ray beam `toward said target, .means.for producing scanning deection of said beam .to cover abidimensionalpattern, two pairs-of oppositely disposed coils, each pair.of coils being positioned on an axis substantially at rightangles tothe axis of the other pair of coils, .a mounting for said coilssurrounding said tube and being rotatable with respect thereto, terminalconnections for supplying said coils with unidirectional current Wherebythe locusv ofthe scanning pattern of the beam with respect to the targetmay be adjusted, means for supplying one pair `of coils with alternatingcurrents of a Wave form similar to that which producesone coordinate ofthe scanning movement of the beam, means to provide the other pair ofcoils ,with alternating currents of a Wave form similarto that whichproduces the other coordinate V of scanning movement of the beam-saidpairs of coils being rotatable `as ya unit with saidmounting Wherebytheportion of the lbeamadjacent to the target is brought.normal-tothetargetat the edges of the target-the magnetccomponents produced by saidalternating vcurrents -insaid coils further influencing the angle ofapproach of said beam to said target adjacent the edgesof said pattern.

-STANLEY V. FORGUE.

REFERENCES CITED The following references are of record in the le ofthis patent:

.UNITED STATES PATENTS Number Name Date l2,102,421 Kuehni Dec. 14, 19372,172,395 McSpadden Sept. 12,1939 2,213,176 Rose Aug."27, v194:02,213,177 Iams Aug. 27, 19,40 2,224,933 vSchlesinger Dec. 17, `19402,227,080 Goldsmith Dec. 31, 1940 2,288,402 Iams 'June 30, 1942 FOREIGNPATENTS Number Country Date 548,697 Great Britain Oct. 21, 1942

